The present application is based on and claims priority from Japanese Patent Applications 2000-297212, filed Sep. 28, 2000 and 2001-139036, filed May 9, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a voltage regulating system of a vehicle AC generator.
2. Description of the Related Art
It is well known that a vehicle AC generator generates small AC voltage (hereinafter residual-field-voltage) due to residual magnetism, even when field current is not supplied to a field coil as long as a rotor of the AC generator rotates. U.S. Pat. No. 5,376,876 discloses a device for detecting rotation of a rotor by making use of such residual-field voltage. However, if leak current flows into an armature winding from a DC power line of higher potential, the device can not detect such residual-field-voltage correctly.
WO99/07064 proposes another device for detecting the rotation of a rotor. This device uses a window comparator so that the rotation can be detected by changing the threshold value thereof. However it takes considerable time to detect the rotation. JP-A-3-215200, which corresponds to U.S. Pat. No. 5,182,511 and EP0484436, or PCT National Application 8-503308, which corresponds to U.S. Pat. No. 5,602,470 and WO95/05606, discloses a device for detecting the rotation in which a voltage difference between two phase-windings is detected to cancel the influence of the leak current. However, it is necessary to provide another complicated circuit for inputting voltage of two phase-windings to a regulator. Because the device disclosed in JP-A-3-215200 detects the voltage difference between two phase-windings under floating condition, it is difficult to set the reference potential of a comparator.
Therefore, a main object of the invention is to provide a simple voltage regulating system that can accurately detect the residual-field-voltage without delay so that the rotation of a rotor can be timely and accurately detected.
According to a main feature of the invention, a voltage regulating system of an AC generator for charging a battery includes a rotor having a magnetic poles therewith, a field coil, an armature winding, a full-wave rectifier unit connected to the armature winding, a rotation detection unit, a voltage control unit for controlling current supplied to the field coil. The rotation detection unit includes a comparator connected to the armature winding, a first circuit for providing a first threshold voltage that is higher than negative side voltage of the battery and lower than a half of the nominal battery voltage and a second circuit for providing a second threshold voltage that is lower than the nominal battery voltage and higher than a half of the nominal battery voltage. The comparator compares the output voltage with the first threshold voltage or the second threshold voltage.
Therefore, the rotation detection can be carried out by a simple circuit structure using residual magnetism of the rotor without delay.
According to another feature of the invention, the rotation detection unit includes a clamp switch which clamps the output terminal of the armature winding at a prescribed potential level; and the comparator compares the output voltage with the first threshold voltage when the clamp switch turns on and with said second threshold voltage when the clamp switch turns off.
Therefore, if leak current flows from a high potential portion such as the positive terminal of the rectifier unit, the clamp switch is turned on to discharge the leak current to a ground, thereby suppressing the potential of the output terminal of the armature winding from rising or floating. As a result, residual field voltage induced in the armature winding can be accurately detected, so that the rotation of the rotor can be accurately detected.
According to another feature of the invention, the rotation detection unit includes a clamp switch for clamping the output terminal of the armature winding at a prescribed potential level, a first comparator for comparing the first threshold voltage with the output voltage of the armature winding when the clamp switch both turns on and turns off, and a second comparator for comparing the second threshold voltage with the output voltage of the armature winding when the clamp switch turns on and when the clamp switch turns off.
Therefore, the rotation of the rotor can be detected whether the clamp switch turns on or not, and whether leak current exists or not.
According to another feature of the invention, the voltage regulating system further includes a first resistor, connected in parallel with the clamp switch. The resistor connects the output terminal of the armature winding and a lower-side terminal of the full-wave rectifier unit.
Therefore, the rotation can be detected under stable conditions.
According to another feature of the invention, the voltage regulating system further includes a second resistor connected in series with the clamp switch between the output terminal of the armature winding and a lower-side terminal of the full-wave rectifier unit.
Therefore, the resistor can suppress leak current, so that the clamp switch can be protected. Preferably, the second resistor has a lower resistance than the first resistor.
According to another feature of the invention, the voltage regulating system further includes a circuit for supplying assisting field current for a predetermined assisting period if the output voltage of the armature winding becomes higher than a threshold voltage. Preferably, the circuit for supplying assisting field current intermittently supplies the assisting field current. Moreover, the circuit stops supplying the assisting current after the assisting period for a period longer than the assisting period.
Therefore, the rotation can be detected accurately even at a very low rotation speed without power loss.